1. Field of the Invention
The present invention relates to an optical lens system for taking image, and more particularly to a miniaturized optical lens system for taking image used in a mobile phone camera.
2. Description of the Prior Art
In recent years, with the popularity of the mobile phone camera, the optical lens system for taking image has become thinner and thinner, and the electronic imaging sensor of a general digital camera is typically a CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) sensor. Due to advances in semiconductor manufacturing, the pixel size of sensors has been reduced continuously, and miniaturized optical lens systems for taking image have increasingly higher resolution. Therefore, there's increasing demand for image quality.
A conventional mobile phone camera usually consists of three lens elements: from the object side to the image side: a first lens element with positive refractive power, a second lens element with negative refractive power and a third lens element with positive refractive power, such as the optical lens system for taking image described in U.S. Pat. No. 7,145,736.
As the pixel size of electronic imaging sensors gradually becomes smaller and smaller, the system requires higher image quality. The conventional optical lens system consisting of three lens elements cannot satisfy the requirements of higher resolution optical lens systems.
An optical lens system for taking image disclosed in U.S. Pat. No. 7,277,238 consists of four lens elements and has a better resolution. However, the fourth lens element is a positive lens element in such a manner that the principal point is located close to the image side of the system, so the back focal length is longer than that of the telephoto type optical lens system whose fourth lens element is a negative lens element. In addition, only the fourth lens element in the optical lens system is negative, so it is poor for correcting the Petzval Sum of the system, making it more difficult to control image quality.
The present invention mitigates and/or obviates the afore-mentioned disadvantages.